Our love of pesticides has been nothing short of disastrous for our insect friends, the honeybees along with the bumblebees and other wild native bee species. Two recent scientific studies point to modern pesticides as the main culprit for the often dramatic declines in both domestic honeybees, Apis mellifera, as well as native wild bee populations.

The pesticides in question are the neonicotinoids, a family of pesticides that are chemically related to nicotine. The neonicotinoids are the first new class of insecticides introduced in the last 50 years. Instead of carrying out their deadly effects by coating the surfaces of a plant's leaves and stems, neonicotinoids are taken up by and circulated inside flowering plants. When a bee collects nectar and pollen, she also sips a dose of these pesticides.

Neonicotinoids are so-named because they act as nicotinic acetylcholine receptor agonists, binding to and activating these neural receptors, causing paralysis and death. This class of pesticides are the most commonly and widely used in the world, used both by large-scale agricultural operations as well as in home gardening products.

Two independent studies show that even low doses of neonicotinoid pesticides can impair bees' navigation abilities, reduce the growth of bee colonies and reduce the number of new queens produced.

The first study (doi:10.1126/science.1215039) conducted by a group of researchers at the French National Institute for Agriculture Research, reports that significant proportions of free-ranging honeybee foragers treated with a nonlethal dose of thiamethoxam, a neonicotinoid systemic pesticide, failed to return to their home hive. In one particular experiment, the researchers attached an RFID chip to their honeybees (see featured image at top) and monitored their comings and goings using a chip reader installed on the hive entrance (image not shown here). The team found a significantly lower forager return rate for honeybees that had been exposed to nonlethal doses of thiamethoxam:

Losing such a large proportion of individual free-ranging forager honeybees places the entire colony at risk of collapse -- and this doesn't consider the loss of bees that suffer lethal doses of pesticides!

The second, complementary, study focused on another neonicotinoid pesticide, imidacloprid, which is currently the most commonly and widely used pesticide in the world. This study, conducted by a group of researchers from the University of Stirling and Lancaster University in the UK, focused on the bumblebee, Bombus terrestris. In their study, the researchers treated colonies of bumblebees with either a low dose or a high dose of imidacloprid, and then weighed the bumblebee colonies each week over an eight week period of time:

As you can see in the figure above, the change in average weight over time for controls (short-dash line) versus low-dose (solid line) and high-dose (long-dash line) colonies was significant: both the low- and high-dose treatment colonies were smaller compared with untreated control colonies.

The British group then examined how many new bumblebee queens are produced by colonies after exposure to either low- or high-dose treatments of imidacloprid:

They found that the number of new queens produced by the control colonies was dramatically greater than the number produced in both low- and high-treatment colonies.

Taken together, these data present a rather damning portrait of our fondness for pesticides, particularly the modern new neonicotinoids. Not only do bee colonies suffer a significant reduction in growth, but forager bees exposed to even low doses of neonicotinoids are not as likely to find their way home. Further, even if these struggling bee colonies survive, they have an 85% reduction in their production of new queens compared with untreated control colonies.

So in short, use of any neonicotinoid pesticide appears to spell out imminent doom for honeybees, bumblebees and their wild kin -- all of which are essential for the continuing survival of flowering plants. Since humans and other animals depend upon flowering plants and their fruits for our survival, the common and widespread use of these pesticides appears to threaten us all.